Marking an autoload constant as a private_constant makes them seem uninitialized. Test case:

test.rb:

class Foo
  autoload :Bar, 'bar'

  private_constant :Bar

  def self.bar
    Bar
  end
end

p Foo.bar

bar.rb:

puts "loading bar"
Bar = "fubar"

jruby -I. test.rb
NameError: uninitialized constant Foo::Bar
  const_missing at org/jruby/RubyModule.java:4867
            bar at const2.rb:8
         <main> at const2.rb:12

If it runs it should show:

loading bar
"fubar"

What is interesting is there is no "loading bar" print so I will guess that marking Bar private is preventing the autoload from firing.

Note that this does not affect JRuby 9.4. Only 10.0.x